The invention relates to an infinitely variable traction roller transmission in which power is transmitted through traction rollers pivotally supported in a housing between toric input and output discs.
In such transmissions, the traction rollers are mounted on support structures which, when pivoted, cause engagement of the traction rollers with the toric discs in circles of varying diameters depending on the desired transmission ratio. The pivotal traction rollers are so supported that they can be moved axially for initiating a change in the transmission ratio. For example, two traction rollers may be supported opposite one another by flexible tension sheets as shown in U.S. Pat. No. 4,086,820 which issued May 2, 1978 to Charles E. Kraus.
In the arrangement according to U.S. Pat. Nos. 4,484,487 and 4,576,055 also assigned to the assignee of the present application, the traction roller support structure is hydraulically supported directly on the housing so that the support structure is not subjected to bending forces. Pivoting of the opposite roller support structures for appropriate transmission ratio positions may be coordinated by an interconnecting ribbon as shown in U.S. Pat. No. 4,086,820, for example.
In the arrangement according to the present inventor's U.S. Pat. No. 4,702,118 the traction roller support members are pivotally supported with respect to the transmission housing by means of antifriction bearing segments which are disposed at opposite ends of the support members and directly mounted on the housing. Although this arrangement is good, the bearing segments are quite expensive and therefore the arrangement as a whole becomes too expensive for small transmissions.
Furthermore, in many small transmissions the power is usually transmitted in the same direction, that is, from one toric disc, the input disc, to the other toric disc, that is, the output disc. In many applications, the output disc torque is the highest at relatively low output disc speed, that is, when the traction rollers are tilted so as to engage the output disc at a large contact circle and the input disc at a small contact circle, and it is the lowest at relatively high output disc speed, that is, when the traction rollers are tilted so as to engage the output disc at a small contact circle and the input disc at a large contact circle. With the larger torque being transmitted at relatively low output disc speed, the traction rollers need to be forced into firmer engagement with the traction discs at low transmission output speeds than at high transmission output speeds where unnecessarily large contact forces would only reduce transmission efficiency and transmission life.
It is therefore the principal object of the present invention to provide a relatively inexpensive infinitely variable traction roller transmission wherein the traction rollers are forced into engagement with the respective traction discs by relatively inexpensive structures and, for some applications, preferably with an engagement force which depends on the pivot position of the traction rollers, that is, which is relatively high in a potential high-torque transmission pivot position and which is relatively low in the opposite end pivot position in which the maximum torque transmitted is relatively low.